The process and advantages of gasifying hydrocarbonaceous material into synthesis gas are generally known in the industry. In high temperature gasification processes, synthesis gas is commonly produced from gaseous combustible fuels, such as natural gas, liquid combustible fuels, and solid combustible organic fuels, such as coal, residual petroleum, wood, tar sand, shale oil, and municipal, agriculture or industrial waste. The gaseous, liquid or solid combustible organic fuels are reacted with an oxygen-containing gas, such as air, enriched air, or nearly pure oxygen, and a temperature modifier, such as steam, in a gasifier to obtain the synthesis gas.
In the reaction zone of the gasifier, the contents will commonly reach temperatures in the range of about 1,700xc2x0 F. (930xc2x0 C.) to about 3,000xc2x0 F. (1650xc2x0 C.), and more typically in the range of about 2,000xc2x0 F. (1100xc2x0 C.) to about 2,800xc2x0 F. (1540xc2x0 C.). Pressure will typically be in the range of about 1 atmosphere (100 KPa) to about 250 atmospheres (25,000 KPa), and more typically in the range of about 15 atmospheres (1500 Kpa) to about 150 atmospheres (1500 KPa).
In a typical gasification process, the synthesis gas will substantially comprise hydrogen (H2), carbon monoxide (CO), and lessor quantities of impurities, such as water (H2O), carbon dioxide (CO2), carbonyl sulfide (COS), hydrogen sulfide (H2S), nitrogen (N2) and argon (Ar). A quench drum located below the reaction zone of the gasifier is used to cool the synthesis gas and remove any solids, particularly ash and/or slag and the particulate carbon soot leaving the reaction zone of the gasifier. In the quench drum, the synthesis gas is passed through a pool of water and exits the quench drum through an outlet nozzle above the water level. The solid particulates settle in the bottom of the drum and are removed. Meanwhile, quench water is continuously removed and added to the quench drum so as to maintain a steady liquid level in the drum.
The synthesis gas is commonly treated to remove or significantly reduce the quantity of impurities, particularly H2S, COS, and CO2 before being used in a downstream process. The synthesis gas is produced for a variety of useful processes, such as producing hydrogen for refinement, carbon monoxide for chemicals production, or producing fuel gas for combustion turbines to produce electricity.
Generally, the heavier the feed, the higher the carbon to hydrogen ratio. A high C/H ratio means that the temperature in the reaction zone of the gasifier will be hotter than when feeds of a lower C/H ratio are gasified. Thus, the use of a temperature moderator, usually steam, water or an inert gas such as carbon dioxide, is required to moderate the temperature in the reaction zone of the gasifier. Water commonly serves as both the carrier and the temperature moderator for solid fuels. Water is also commonly mixed with liquid hydrocarbon fuels. Steam may also be introduced into the gasifier in admixture with either the feed, the free-oxygen containing gas stream, or both.
Generally, a portion of the quench water removed from the quench drum of a gasifier is processed in a downstream unit and recycled back to be mixed with the feed to the gasifier. In most cases, the mixing of the quench water and the feed does not cause any problems. When liquid feedstocks are so heavy that they need to remain heated so as to keep their viscosities down to pumpable levels, however, the mixing of the quench water with the feedstocks is no longer practical.
Viscosity also plays an important part in the conversion of the feedstock in the gasifier. Generally, it is desirable to atomize the feed in order to spray fine particles into the reactor. The finer the particles, the higher the conversion will be. It is difficult, though, to atomize materials with high viscosities into fine particles, and the addition of water can produce non-homogeneous mixtures. Thus, mixing water with a high viscosity feedstock can also adversely affect conversion in the gasifier if mixing is poor.
The present invention provides a process whereby a liquid hydrocarbonaceous material of high viscosity is fed to a gasifier for conversion to synthesis gas. The feedstock, steam, oxygen containing gas, and recycled quench water are all fed into the gasifier through a four stream feed injector. The feedstock in this design is sandwiched between two oxygen streams so as to provide better atomization of the exceptionally heavy feed and, hence, better conversion to synthesis gas. The central bayonet of the feed injector provides a flow path for the fourth stream, the quench water recycle. This arrangement avoids mixing and cooling the feedstock that would increase the viscosity and thereby lower conversion in the gasifier.